Method and appabatus foe landing



May 23, '1944. w. -r COOKE ETA L Re; 22,

I METHOD AND APPARATUS FOR LANDING AIRCRAFT I Original Filed Aug 28, 1940 INVENTORS William T Cooke Abbof' 5.-Maed.er

ORNEY Reissued why-23, 1944 p Re. 22,484

METHOD AND APPARATUS roa manure smcmr'r William T. Cooke, Garden City, N. Y., and Abbott S. Maeder, deceased, by Sperry Gyroscope Company, Inc., assignee, Brooklyn, N. Y., a corporation of New York .Original No. 2,307,023, dated January 5,1943, Se-

rial No. 354,498, August 28, 1940. Application for reissue September 1, 1943, Serial No. 500,812

18 Claims. ('01. 250-11) This invention relates, generally, to the blind landing of aircraft, and the invention has reference, more particularly, to, a novel method and means including an automatic ratio control 518- nal receiver for use in connection with overlapping radio beams for efiecting the blind landing of aircraft, the receiver. serving to differentially amplify the signals of the radio beams, whereby a desired artificial guide path is obtained.

Ultra high frequency directive radio beams of the order of cycles per second are employed in the blind landing apparatus of this invention. The beams used, for example, may be differently modulated and provide an overlapping zone or guide path down which the aircraft flies during landing. At these high frequencies the guide path provided by the beams is substantially straight, so that if the craft follows the beam path all the way down, there is a tendency for the craft to fiy into the ground. It is desirable, of course, to provide a straight guide path for the major portion of the landing operation, but just before the craft reaches the ground it is preferable to flatten or curve the glide so that the craft will land smoothly.

The principal object of the present invention is to provide a novel method and means for effecting the blind landing of aircraft which provides a substantially straight glide path for the greater part of the landing operation and with the path altered prior to landing to afford optimum'landing conditions.

Another object of the present invention is to provide a novel ultra high frequency signal control receiver that serves to automatically flatten out or otherwise vary the glide path for the craft as the landing point is approached to thereby obtain optimum landing conditions, this being accomplished by automatically changing the amplification ratio of the two, overlapping transmitted glide path signals at the'receiver.

Other objects and advantages will become apparent from the specification, taken in connection with the accompanying drawing wherein one embodiment of the invention is illustrated.

In the drawing,

Fig. 1 is a wiring diagram of this invention, and v Fig. 2 is a schematic view of the apparatus of this invention providing an artificial landin path.

Referring now to the drawing illustrating the invention, the reference numeral l designates a receiving antenna carried by the aircraft, which of. the novel receiver antenna feeds into an ultra high frequency radio amplifier and detector 2. In the amplifier and detector 2 the ultra high frequency modulated signals, received from the overlapping landing beams II and 22 (Fig. 2) that have different modulating frequencies FI and F2, are superimposed upon a suitable carrieror locally generated frequency andthen detected to produce an intermediate frequency signal which is supplied to the intermediate frequency amplifier shown as consisting of two stages 3 and 4. Automatic volume control bias is supplied to amplifier stages 3 and 4 from the-AVG detector 5 which is supplied from the intermediate frequency amplifier 6 operating at a constant gain. This will be understood when it is noted that the bias on the control grid of tube 6 is determined by resistance I inserted between this grid and ground line 23, whereas the bias on the control grids of tubes 3 and l is determined by resistances 8 and 9 connected to the AVG line In, the potential of which is determined by lead ll connected to the filtered output of AVG detector or diode rectifier 5.

The output of the intermediate frequency amplifier l is detected by a second detector I2 and further amplified by a tube It, the output of which supplies band pass filters l4 and i5, respectively, passing frequencies Fl and F2, which select the respective modulations of the two overlapping beams. The automatic volume control line It is also-connected to the control grid of audio amplifier l0, whereby the automatic volume control bias controls the gain of this amplifier which amplifies the signal of one beam. such as that transmitted by one radiating horn -or emitter 21. The audio amplifier II amplifies the signal supplied from filter l5, 1. e., the signal of the other beam transmitted from horn or emitter 24', and this amplifier ll operates at constant gain since the bias on its grid is determined by resistance 32 connected to the ground lead 23. The outputs of the tubes l6 and I! are connected in opposition and pass through audio transformers 20 and ii and through copper oxide rectifiers 25 and 2b for application to the up-down or zero center microammeter 21.

The operation of the system of this invention in providing an artificial glide path that is variable at will by varying the AVG will be understood from Fig. 2. In this figure, the overlapping beams' II and 22 provide a glide path indicated by the dotted line 28, i. e., a straight glide path down which the craft would normally fiy to earth 30. In using the novel receiver of this invention, however, and assuming it is desired to flatten out the'glide path just before landing to prevent flying the craft into the ground, the detected modulation Fl of the upper beam 2| is amplified by the tube l6 having AVC bias thereon whereas the F2 signal of the lower beam 22 is amplified 'by tube ll operating at constant gain. Thus, .the signal of the upper beam is weakened relative to that of the lower beam and in" order to fly in an equi-signal region, the pilot must alter his course as shown by the solid line ll, thereby automatically flattening his glide to provide a normal landing. Although, in the exe ample given the effective glide path is raised as the craft approaches a landing, this path could along its path defined as the equi-signal zone of the intersecting lobes or directive radiation patterns, according to the orientation of the lobes or patterns and the pointer of meter 21 is in a neutral position, indicating that the strength of the signals derived from the modulation components as applied to the meter are equal and hence have a unitary relative strength ratio.

The foregoing operation is modified, accord ing to the present invention by unbalancing this ratio, as a function of the total received field strength, as by varying the fly-up or fly-down signals, in the case of instrument landings. This results in unequal opposed signals at the meter and causes a meter deflection that requires a, displacement of the craft in a direction to restore the unitary ratio, thereby providing a new path displaced from and convergent on the original path. If the ratio is continuously and progressively unbalanced as a function of the distance of the craft from the transmitter, determined, for example, as a function of the combined lobe field strength as measured by the AVG bias, the new path becomes less convergent, parallel, or even divergent relative to the original ath, according to the manner in which the signals are unbalanced Unbalancing the respective signal strengths, as indicated, accordingly diverts the craft and alters the apparent locus of the original flight path as the craft nears the transmitten As many changes could be made in the above varies from a straight line as the landing area is approached.

2. In apparatus for landing aircraft, ultra high frequency radio projecting means in the region of the landing area producing overlapping beams of differently modulated electromagnetic energy,

and a receiver carried by the aircraft, said re ceiver comprising amplifiers for amplifying the modulations of the beams, and an automatic volume control detector circuit connected for limiting the gain of an amplifier of one of said modulations, the amplifier of the other modulation of such signal. rectifying said thusly amplified signals, andflying the aircraft such that the rectified signals are equal.

4. An ultra high frequency receiver for aircraft in effecting blind landings comprising, means for superimposing l'eceived ultra high frequency signals upon a locally generated frequency and for detecting said signals to produce intermediate frequency signals, an automatic volume control amplifier connected for amplifying said signals, an intermediate frequency detector connected for detecting said intermediate frequency signals, audio amplifiers connected for amplifying said detected signals, and means for varying the ratio of the gains of the audio amplifiers in accordconstruction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof,

it is intended that all matter contained in the above description or shown in the accompanying drawing shall beinte'rpreted as illustrative and not in a limiting sense.

Having described our invention what we claim and'desire to secure by Letters Patent is:

1. In apparatus forlanding aircraft, ultra high frequency radio projecting means in the region of the landing area producing overlapping beams of electromagnetic energy, means for modulating said beams at different frequencies, a receiver carried by the aircraft, said receiver comprising different amplifiers for amplifying the different modulations of the beams, and meanscontrolled by the strength'of the received energy for varying the amplification ratio between said different amplifiers, thereby providing a glide path that ance with the strength of the received signals, and means for indicating the difference in the relative strengths of said amplified modulations.

5. An ultra high frequency receiver for aircraft in effecting blind landings comprising, means for amplifying the received diflerentlv modulated signals, means for detecting said signals, automatic volume control means, amplifiers for amplifying said respective modulations, one of said amplifiers being controlled from said automatic volume control means so that said modulations are amplified in different ratios depending upon the strength of the received signals, rectifier means for rectifying said simplified modulations, and means for comparing the relative strengths of said rectified modulations.

6. In an apparatus for landing aircraft, ultra high frequency radio projecting means in the region of the landing area producing overlapping beams of differently modulated electromagnetic,

energy, means on the aircraft for receiving said differently modulated energy, means for detecting .said received energy to obtain the modulations therefrom, means for separating said modulations, means for amplifying one of said modulations at constant gain and the other at varying gain depending on thestrength of such modulation, and indicator means supplied with said amplified modulations in opposition.

7. In a method of guiding a craft with refer-.

ence to a path defined by the equl-signal zone of a pair of overlapping lobes of directive radiation in response to equal amplitude signals derived from said respective lobes, the step comprising altering the apparent orientation of said path by unbalancing the unitary amplitude ratio 9. In a method of guiding a craft with refer 'ence to a glide path defined by the equi-signal zone of a pair of overlapping lobes radiated directively from a transmitter, along which path upwardly-directing and downwardly-directing signals derived from said lobes are of equal amplitude, the steps comprising unbalancing the unitary ratio of said amplitudes progressively as a function of the field strength received from the combined lobes, and regulating the craft motion relative to said path so as to restore said ratio.

10. In a method of guiding a craft using as a reference a guide path defined by the equi-signal zone of a pair of overlapping lobes of directive I radiation, the steps comprising deriving signals as a function of the relative field intensities of the respective lobes, maintaining said craft substantially on said path so as to maintain said signals of equal amplitude, progressively unbalancing the unitary ratio of said amplitudes as said craft approaches the source of said radiation in response to a predetermined function of field strength of the combined lobes, and thereupon diverting said craft from said path to restore said ratio.

ll.- In apparatus for landing aircraft, ultra high frequency radio projecting means in the region of the landing area producing overlapping beams of electromagnetic energy, means for modulating said beams at different frequencies, a receiver carried by the aircraft, said receiver comprising means for deriving signals from the modulation component of each of said beams, and means controlled by the strength of the received energy for varying the amplitude ratio between said respective derived signals, thereby providing a. glide path that varies from a straight line as the landing area is approached.

12. An ultra high frequency receiver for aircraft in effecting instrument landings along a path defined by differently modulated intersecting radiant energy lobes, comprising means for amplifying the received differently modulated signals, means for detecting said signals, automatic volume control means, means for deriving fly-up and fly-down signals from said detected signals, means for controlling the strength of said flyup signals relative to said fly-down signals in response tosaid volume control means, and means for indicating whether said signals are of equal strength.

13. In anapparatus or landing aircraft, radio frequency energy projecting means in the region of the landing area producing overlapping beams of differently modulated electromagnetic energy,

means on the aircraft for receiving said differentiy modulated energy, means for detecting said received energy to obtain the modulations therefrom, means for separating said modulations,

means for amplifying said modulations, indicavarying said relative strength as a function of the combined field strength of said patterns.

15.'A radio receiver for a craft following a path defined by the equi-signal zone of a pair of intersecting distinctively-modulated directive radiation patterns, comprising means for detecting the modulation component of each oi'said patterns, an automatic volume control generator( means for indicating th relative strength of said respective detected components, and means for varying said relative strength as a function of the output from said generator.

16. .A radio receiver for a craft following a pathdefined by the equi-signal plane of a pair of intersecting distinctively-modulated directive patterns radiated from a transmitter, comprising means for detecting the modulation component of each of said patterns, means for deriving flyup and fly-down signals therefrom, means for comparing the relative strengths of said fly-up and said fly-down signals, and means for automatically progressively varying said relative strengths as said craft approaches said transoverlapping directive radiation patterns while I said aircraft proceeds along the equi-signal zone of said patterns, a glide-path indicator energized by said signals in opposition, thereby providing a neutral indication when said signals ar equal, means for deriving a potential as a function of the field strength of said combined radiation patterns, and means for applying a function of said potential to said indicator, thereby shifting said indication from said neutral indication.

18. An instrument landing receiver for aircraft, comprising means overlapping directive radiation patterns while said aircraft proceeds along the equi-signal zone of said patterns, a glide-path indicator energized by said signals in opposition, thereby providing a neutral indication when said signals are equal, and means for biasing said indicator as a function of thefleld strength of at least one of said radiation patterns.

for deriving signals m two I 

